1. The Field of the Invention
The present invention relates to methods for separating particulate matter from a fluid stream using a centrifugal separator.
2. The Relevant Technology
Water purification is an age-old activity that has been pursued to achieve both potable water and water for industrial use. With the rise of industrialization, water purification took on a new importance because industrial water usage generally involved discharging contaminated water into the environment. As concerns about the environment have increased, water discharged into the environment has been subjected to increasingly higher standards. Thus, increased efforts have been undertaken to identify methods of processing water to substantially reduce both dissolved and particulate pollutants.
One aspect of water purification that is particularly time consuming and/or equipment intensive is liquid-solid separation. Traditionally, settling ponds, or thickeners, have been used in which a large volume of particulate-containing water is allowed to reside in a quiescent state. With the force of gravity acting on the mixture, the particulate, even those in the Stokes flow regime, will separate from the liquid.
One disadvantage to the use of thickeners is that they have to be extremely large to have any significant flow capacity. Thus, their use is not practical in crowded urban areas where the need for such water purification systems is often the greatest. Consequently, thickeners have been developed that allow for a continuous flow of particulate-containing liquid into the center of the thickener, producing a clarified supernatant liquid and a compacted sludge. The compacted sludge, exiting from the bottom of the thickener, typically has a water content that amounts to between 10 and 30 percent of total water being fed to the thickener.
Traditional thickeners have been improved in the last decade or so with the advent of the high-rate thickener. The high-rate thickener has a center feed well that extends below the mud line of the underflow material. Accordingly, all water entering the thickener must pass through the sludge which acts as a filter medium. By using the sludge as a filter, solid-liquid separation rates are increased, albeit only incrementally over that of traditional thickeners. Additionally, high-rate thickeners also must be very large and, consequently, also have large footprints, rendering their use impractical in many situations.
Another aspect of separation includes liquid-liquid systems such as separating the oil and water from a sump in a machine shop or in a washing bay for trains or buses, etc. Other liquid-liquid separation systems are utilized in the food industry where oil and water need separation. One of the problems in the prior art is the effect of load disturbances such as a surge of oil or water in a cleaning operation that upsets the balance of the oil/water feed ratio to the separator. Although the separator may be controlled to prevent one component from entering the wrong exit stream, a catastrophic surge of one component or the other cannot be controlled.